1. Field of the Invention
The present invention relates generally to electrolytic pool chlorinators for chlorinating a pool of water, and more particularly, to an electrolytic pool chlorinator having anode and cathode chambers to which fresh pool water is continuously added to automatically maintain the fluid levels of the anolyte and catholyte within the anode and cathode chambers, respectively.
2. Description of the Prior Art
Electrolytic pool chlorinators are well known in the art and are exemplified by the apparatus described in the following U.S. Pat. Nos. 914,856, issued to Meyer; 3,223,242, issued to Murray; 4,229,272, issued to Yates; 4,129,493, issued to Tighe, et al.; 4,136,005, issued to Persson, et al.; 4,290,873, issued to Weaver; and 4,500,404, issued to Tucker. Such electrolytic pool chlorinators generally operate by electrolyzing a sodium chloride solution contained within an anode chamber, attracting positively charged sodium ions to a negatively charged cathode and liberating chlorine gas at the anode. The chlorine gas released thereby may then be used to chlorinate the water within a swimming pool, spa or the like.
The anode and cathode chambers of such an electrolytic pool chlorinator are typically separated from one another by an ion-permeable barrier to prevent the chlorine gas liberated within the anode chamber from mixing with the hydrogen gas liberated in the cathode chamber and to physically separate the sodium chloride (or brine) anolyte solution within the anode chamber from the sodium hydroxide ( caustic soda) catholyte solution within the cathode chamber. The ion-permeable membrane is permeable to positive ions, such as sodium ions formed within the anode chamber, but presents a barrier to the passage of negative ions, such as hydroxyl ions, present within the cathode chamber, at least at relatively low concentrations of such hydroxyl ions.
While electrolytic pool chlorinators of the type described above greatly simplify swimming pool maintenance by eliminating the need to regularly add chlorine to the pool water, as by adding chlorine in solid, liquid or gaseous form at regular intervals, known pool chlorinators are not themselves maintenance free. The brine solution within the anode chamber becomes depleted over time and must be replenished. Even if the anode chamber is made rather large to accommodate a large quantity of solid salt, water must periodically be added to the anode chamber to continuously dissolve such salt to form the brine solution.
Similarly, the level of fluid within the cathode chamber must also be maintained, and the concentration of sodium hydroxide within the catholyte must periodically be reduced, as by substantially draining the cathode chamber and refilling the same with water. If the concentration of hydroxyl ions within the cathode chamber becomes excessive, back-migration of hydroxyl ions through the ion-permeable barrier will result, decreasing the efficiency of the chlorinator and causing other problems described in greater detail below. Many of the prior art chlorinators require the user to periodically drain the cathode chamber and to refill it with water to avoid excessive accumulations of sodium hydroxide within the cathode chamber.
Prior art chlorinators are known wherein attempts have been made to simplify maintenance requirements for filling the anode and cathode chambers. For example, U.S. Pat. No. 4,229,272 issued to Yates illustrates a pair of manually operated valves which may be used to fill the anode and cathode chambers of the chlorinator with fresh pool water. Nonetheless, the user must remember to periodically operate such manual valves, or they will otherwise be of no benefit to the user. U.S. Pat. No. 4,500,404 issued to Tucker automatically suppplies water to both the anode and cathode chambers of the electrolytic chlorinator described therein. However, the Tucker apparatus requires a supply of tap water, rather than pool water, for filling the anode and cathode chambers and further requires a water softening resin chamber within the chlorinator to further reduce the hardness of the incoming tap water. While this apparatus serves to eliminate the maintenance chore of filling the anode and cathode chambers, the user must then periodically service the resin chamber by recharging the softening resin.
U.S. Pat. No. 3,563,879 to Richards, et al. discloses an electrolytic chlorine generator wherein pressurized pool water is in fluid communication with the anode and cathode chambers of the chlorine generator. However, as electrolysis proceeds within the chlorine generator, the pressure of the chlorine gas in the anode chamber and the hydrogen gas in the cathode chamber rise to a pressure exceeding that of the pressurized pool water. Consequently, no water is added to the anode or cathode chambers during operation of the chlorinator. Only after the pool circulating pump and the power supply to the chlorinator are turned off, and the pressure within the anode and cathode chambers dissipates, can fresh pool water be pumped into the anode and cathode chambers when the pool pump is restarted.
U.S. Pat. No. 4,136,005 issued to Persson, et al. describes an electrolytic pool chlorinator wherein a brine source is provided apart from the anode chamber of the electrolytic cell. A discontinuous water metering device incorporating a solenoid valve, and related electronic controls, is provided for intermittently feeding pool water to the brine source, and to the cathode chamber of the electrolytic cell. While the apparatus disclosed in the Persson, et al. patent serves to maintain the proper levels of anolyte and catholyte within the electrolytic cell, the requirements for a separate brine source and the complexity of the water metering device are disadvantageous.
Accordingly, it is an object of the present invention to provide an electrolytic pool chlorinator which automatically maintains the proper level of anolyte and catholyte within the anode and cathode chambers, respectively, without reliance upon the operation of manual valves or periodic interruptions in operation.
It is another object of the present invention to provide a relatively maintenance free electrolytic pool chlorinator which uses pool water to fill and maintain the level of anolyte within the anode chamber, and to fill and continuously dilute the catholyte within the cathode chamber, thereby avoiding the necessity for connection of the chlorinator to a municipal water supply.
It is still another object of the present invention to provide such an electrolytic pool chlorinator which continuously flushes sodium hydroxide from the cathode chamber in order to maintain a relatively low caustic concentration therein.
It is yet another object of the present invention to provide such an electrolytic pool chlorinator which avoids substantial pressurization of the anode and cathode chambers.
It is further object of the present invention to provide such a pool chlorinator which incorporates a relatively large anode chamber having a large salt capacity without requiring a separate brine source.
It is a still further object of the present invention to provide such an electrolytic pool chlorinator which is of relatively simple and inexpensive construction.
As mentioned above, sodium hydroxide is formed within the cathode chamber as a result of the electrolysis process. Excess sodium hydroxide concentrations within the cathode chamber must be avoided to prevent significant amounts of back-migration of hydroxyl ions through the ion-permeable membrane and back into the anode chamber when electrical power is cut off from the electrolytic cell. Since residential swimming pool circulation systems are typically operated less than twelve hours each day, the chlorinator power supply is likely to be off more than it is on, and consequently, back-migration of hydroxyl ions can become significant as concentrations of sodium hydroxide rise within the cathode chamber. The efficiency of an electrolytic pool chlorinator may be reduced in several ways as a result of excessive hydroxyl ion concentration within the catholyte. For known electrolytic pool chlorinators, when hard water, i.e., water containing relatively high levels of calcium, is added to the cathode chamber, calcium deposits typically form upon the cathode, particularly when the hydroxyl ion concentration within the catholyte is high. The formation of calcium deposits upon the cathode causes the cathode to appear more resistive resulting in increased heat dissipation into the electrolytic cell and reduced current efficiency. Furthermore, hydroxyl ions which back-migrate through the ion-permeable membrane often combine with calcium in the anolyte to form chlorates which effectively reduce the amount of sodium chloride which can be dissolved within the anolyte. In addition, the presence of hydroxyl ions within the anolyte can lead to passivation of the anode resulting from increased oxidation which occurs at higher pH within the anolyte. Hydroxyl ions within the anolyte also contribute to the formation of calcium deposits upon the anode side of the ion-permeable membrane, which deposits lead to the plugging of the membrane and a corresponding reduction in the efficiency of the chlorinator.
Those skilled in the art have attempted to deal with the aforementioned problems associated with excessive hydroxyl ion concentration within the catholyte and related calcium deposits. For example, U.S. Pat. No. 4,204,921 issued to Britton, et al. describes the periodic addition of an acid to the catholyte for dissolving calcium deposits from the cathode. U.S. Pat. No. 4,040,919 describes a method of dissolving deposits upon the membrane by increasing the acidity of the anolyte and simultaneously diluting the catholyte while operating the cell at a reduced current density. Clearly, both of the processes described in these patents suffer from the disadvantage of requiring periodic additions of acid to the electrolytic chlorinator.
U.S. Pat. No. 4,115,218, issued to Krumpelt describes a commercial process for the electrolysis of sodium chloride to produce a caustic, and wherein electrolytic cell inefficiencies are reduced by periodically flushing the catholyte compartment and operating the cell at reduced current. However, the process described in this patent requires the use of highly pure brine having a calcium content of six parts per million or less, thereby requiring special processing of the sodium chloride used to form the brine. Furthermore, the requirement for brine of such purity would rule out the use of swimming pool water within the anode chamber of such an electrolytic cell since swimming pool water typically has a calcium hardness of 200-250 parts per million.
U.S. Pat. No. 4,129,493 issued to Tighe, et al. discloses a swimming pool chlorinator having a cathode chamber having an inlet for receiving a supply of deionized water and an outlet for discharging sodium hydroxide. The deionized water is supplied by an ion exchange column coupled to the municipal water supply.
As noted above, U.S. Pat. No. 4,500,404 issued to Tucker discloses a similar apparatus for supplying water to the cathode chamber. While the apparatus disclosed in both such patents minimizes the likelihood of calcium deposits upon the cathode by physically limiting the introduction of calcium thereto, both such systems suffer the disadvantage of not being able to use pool water from the pool being chlorinated in order to dilute the catholyte.
As noted above, U.S. Pat. No. 3,563,879 periodically introduces pool water into the cathode chamber and dilutes the sodium hydroxide therein. However, such pool water is introduced into the cathode chamber only after operation of the chlorinator is discontinued and only after the pool circulation pump is shut off and later restarted. Significant amounts of sodium hydroxide may be left remaining within the cathode chamber between operating cycles of the chlorinator, thus permitting back-migration of hydroxyl ions.
U.S. Pat. No. 4,136,005 issued to Persson, et al. periodically introduces pool water into the catholyte compartment to dilute the catholyte. The cathode compartment includes an overflow passage for allowing excess catholyte to drain from the cathode compartment. However, fresh pool water is discharged into the cathode compartment in relatively close proximity to the cathode. The present inventor has determined that the discharge of relatively hard water into the cathode compartment in close proximity with the cathode induces the formation of calcium deposits upon the cathode due to the highly alkaline localized region surrounding the cathode during operation of the electrolytic cell.
Accordingly, it is an object of the present invention to provide an electrolytic pool chlorinator which minimizes the likelihood of calcium deposits upon the cathode and ion permeable membrane of the electrolytic chlorinator.
It is another object of the present invention to provide such an electrolytic chlorinator which minimizes the likelihood of formation of chlorates within the anolyte and minimizes the likelihood of anode passivation due to high pH conditions within the anolyte.
It is yet another object of the present invention to provide such an electrolytic pool chlorinator which continuously and automatically maintains a relatively low sodium hydroxide concentration within the cathode chamber to minimize back-migration of hydroxyl ions into the anode chamber when the power supply of the chlorinator is shut off.
It is a further object of the present invention to provide such an electrolytic pool chlorinator which avoids the need for specially treated water or specially purified brine and wherein ordinary pool water may be used to continuously dilute the concentration of sodium hydroxide within the cathode chamber.
A further object of the present invention is to provide such a pool chlorinator wherein ordinary pool water may be added to the cathode chamber to dilute the sodium hydroxide concentration therein without simultaneously forming calcium deposits upon the cathode.
The problem of the plugging of the ion-permeable membrane with calcium deposits associated with many known prior art chlorinators has already been noted above. Apart from membrane plugging, the membrane typically requires replacement every two-four years in view of regular wear and resulting tearing of the membrane. Most of the electrolytic pool chlorinators which have been made commercially available or which have been described in the patent literature are not so constructed as to permit the replacement of the ion-permeable membrane in a convenient and inexpensive manner. U.S. Pat. No. 3,972,794 issued to Lamm discloses several configurations of an electrolytic cell for generating chlorine wherein various components of the electrolytic cell are assembled as a removable cartridge, typically including the anode, ion-permeable membrane and other components. The apparatus described by Lamm appears to suffer from several disadvantages, including the need for substantial disassembly of the electrolytic cell to remove the replaceable cartridge, the requirement for replacing more than just the ion-permeable membrane, as well as the requirement for a rather bulky and apparently expensive replacement cartridge. The electrolytic cell described in the Lamm patent does not appear to lend itself to being serviced by the typical owner of a residential swimming pool.
Accordingly, it is an object of the present invention to provide an electrolytic pool chlorinator incorporating an easily replaceable ion-permeable selective membrane capable of being replaced by a typical owner of a residential swimming pool without requiring substantial disassembly of the chlorinator.
It is another object of the present invention to provide such a replaceable membrane in a form which is relatively inexpensive, compact, and easy to handle.
With regard to prior art electrolytic pool chlorinators of the type described above, such chlorinators are typically designed to operate in conjunction with the conventional water recirculation system of the pool. Often, such chlorinators rely upon a pressurized flow of pool water produced by the pool pump in order to intermix liberated chlorine gas with the pool water. Should the electrolytic pool chlorinator continue to operate after the pool pump is turned off, there arises the danger that chlorine gas generated by the chlorinator would either escape into the area surrounding the chlorinator or accumulate under dangerous pressure within the chlorinator.
It is known to connect the power supply for an electrolytic pool chlorinator to the same timer switch which controls the application of electrical power to the pool pump motor for insuring that electrical power to the chlorinator is turned off at the same time that electrical power to the pool pump motor is turned off. However, circumstances may arise wherein the flow of pool water through the circulation system is stopped even through electrical power is being supplied to the pool pump motor; for example, the pool pump motor may either fail or lose its prime. U.S. Pat. No. 4,256,552 issued to Sweeney describes an electrolytic chlorine generator which, in one case, is energized in response to a pressure switch that operates whenever water is circulating through the pool pump recirculation system. No details are provided regarding such a pressure switch. In any event, mechanically operated pressure switches are likely to fail when exposed to relatively hard pool water containing calcium and other minerals.
In view of the foregoing, it is an object of the present invention to provide an electrolytic pool chlorinator of the general type wherein liberated chlorine gas is intermixed with a stream of pool water, which chlorinator terminates the further production of chlorine gas if the stream of pool water is interrupted.
It is a further object of the present invention to provide such a pool chlorinator which inexpensively and reliably senses an interruption in the stream of pool water to terminate the further generation of chlorine gas.
Another problem related to prior art electrolytic pool chlorinators regards the adequate cooling of the power supply which produces the direct current voltage across the anode and cathode elements. Typically, the power supply housing is provided with air vents for allowing air to circulate through and cool the power supply components, primarily the transformer used to convert 110 volt or 220 volt alternating current to a relatively low voltage alternating current and the rectifier which subsequently converts the low voltage alternating current to a low voltage direct current potential. However, the presence of such vents in the power supply housing prevents the power supply from being a sealed unit; consequently, water splashed onto the power supply housing from rain, from the swimming pool, or from hoses used in the pool area can enter the power supply housing and corrode the power supply components.
It is still another object of the present invention to provide such a pool chlorinator which eliminates the need for air circulation vent holes in conjunction with the chlorinator power supply for allowing said power supply to be housed as a sealed unit.
These and other objects of the present invention will become more apparent to those skilled in the art as the description thereof proceeds.